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November 2005

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 16 Nov 2005 16:46:41 EST
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In a message dated 11/16/05 15:21:55, [log in to unmask] writes:
> Couple questions regarding the dreaded lead free process.
> 1.      Do I need to request a different process for PCB fabs, what is
> the difference if any?
> A: It depends. For thin PCBs with components of near-uniform size you may be 
o.k. 
For thicker PCBs and components with significant differences in thermal mass 
you need to specify: hi-Tg/hi-Td/low CTE materials [beware of datasheets--lots 
of wrong info on them] [ you may want to specify STII=>215], you need to 
specify E3 copper foil for internal layers, you need to specify at least 1.2 mils 
of Cu in the through-holes, you need to specify vigorous moisture bakeout 
prior to soldering process.
> 
> 2.      I understand that lead free components require a higher
> temperature and longer reflow time, which may affect other component
> reliability.   Not all the components we use are available for lead free
> processes. Any recommendations on the processes to be used with a
> mixture of leaded vs. lead free? Is this wise? What should we be looking
> out for?
> A: iNEMI has determined that for components the MSL rating drops one level 
for every 10C increase in soldering temperature
> 
> 3.       I did not want to recreate the wheel, anyone have a test plan
> or qualification plan available to qualify this type of process?
> A: Look at IPC-9701A at least for a partial answer.
> 
> 4.    And any recommendations on a lead free process class that we could
> send a few of our technicians to?
> A: Technicians you might send them to some of Bob Willis' courses; Engineers 
and Designers you might send to my workshops [next ones in Boston December 5 
and 6].

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com


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